1. Field of the Invention
The present invention relates to a method for peeling off a semiconductor element formed on an insulating surface and to a method for manufacturing a semiconductor device by using the peeling method.
2. Description of the Related Art
Portable electronic equipment typified by a mobile phone, an electronic notebook and the like require multiple functions such as sending and receiving e-mail, voice recognition, taking-in images by a small camera as well as a flat panel display for displaying images. On the other hand, reduction in size and weight of the portable electronic equipment is still sought for satisfying the user needs. Therefore, as many ICs having larger circuit scale and memory capacity as possible are required to be mounted on the narrow space of the portable electronic equipment. It is an essential part to make a flat panel display to be mounted as thin and light as possible in order to achieve the reduction in size and weight of the portable electronic equipment while making space for mounting ICs. Reducing the thickness of a glass substrate used for forming a display panel is likely to be the most effective means of reducing the thickness and weight of the portable electronic equipment. However, there is a limit in reducing the thickness of a glass substrate when the mechanical strength of the display panel is considered. For instance, in the case where barium borosilicate glass, aluminum borosilicate glass and the like are utilized, a 3 inch square panel has a thickness of approximately 1 to 2 mm and a weight of approximately 10 g at least.
In view of the foregoing, a flat panel display using a plastic substrate instead of a glass substrate has been actively researched and developed. A plastic substrate having flexibility exhibits an excellent resistance to vibration and shock as compared with a glass substrate. In addition, a plastic substrate can be easily reduced in thickness and the material itself is light. Therefore, a plastic substrate is considered to be effective for forming a thin and light flat panel display. However, in many cases, the heat resistance of a plastic substrate is not high enough to withstand a heat treatment during manufacturing steps of a semiconductor element. Thus, a manufacturing method of a semiconductor element is suggested in which another substrate having a high heat resistance is prepared and a semiconductor element is formed thereon, then the semiconductor element is peeled off from the substrate and attached on a plastic substrate. A specific method of the peel-off varies according to manufacturers and each manufacturer exercises its ingenuity in their peeling method.
In Patent Document 1 (Patent Document 1: Japanese Patent Laid-Open No. 2001-223165), a manufacturing method of nitride semiconductor is disclosed. According to this manufacturing method, after a porous GaN layer having a lot of fine voids on the surface is formed on a substrate by photo etching, a GaN epi layer is formed on the porous GaN layer by epitaxial growth. Then, the porous GaN layer having voids is dissolved and fractured by selective etching, high-pressure water, GaAs jet, laser and the like so that the GaN epi layer is peeled off from the substrate and attached to another substrate.
According to the peeling method disclosed in Patent Document 1, before forming a semiconductor layer, voids are formed between a substrate and the semiconductor layer. Hence, after forming the semiconductor layer, a heat treatment, an irradiation of laser beam and the like do not have to be performed on the semiconductor layer with the intention of facilitating the peel-off. Thus, the peeling method above has the advantage that the semiconductor layer is not damaged and the stress within the semiconductor layer can be reduced due to the voids.
However, since the voids are formed by photo etching according to the peeling method disclosed in Patent Document 1, there is a limit in making larger voids. Therefore, it is not possible to appropriately enlarge the voids in order to reduce the time required for dissolution and fracture of a layer on which the voids are formed or to reduce the stress of a semiconductor layer when peeled off. Moreover, although a peeling method of a single crystalline semiconductor layer is disclosed in Patent Document 1, there is no specific description of a peeling method of a thin film semiconductor element on an insulating surface by the use of voids.
In view of the foregoing, it is a general object of the invention to provide a peeling method of a thin film semiconductor element on an insulating surface by the use of voids, and it is another object of the invention to provide a manufacturing method of a semiconductor device by transferring the peeled semiconductor element.